Mottled Duck introductions to South Carolina: The ugly, the bad, and the good?

Abstract Translocations or other movements of wildlife sometimes accomplish their intended objectives, but unforeseen consequences may arise and disrupt locally adapted ecological communities, restructure or dilute genetic integrity of populations or subspecies of the moved organism, and otherwise negatively influences a species’ long‐term fitness. Two historical populations of Mottled Ducks (Anas fulvigula) exist and are endemic to (1) Mexico and the West‐Gulf Coast (A. f. maculosa) regions of the United States and (2) Florida (A. f. fulvigula). From 1975 to 1983, 1285 Mottled Ducks from Florida, Louisiana, and Texas were released to coastal South Carolina, primarily to ultimately establish a legally harvestable population. This movement stirred mixed reactions amid the conservation community. Contemporary information suggests an increasing Mottled Duck population in South Carolina and possibly dispersing into Georgia. Herein, I objectively discuss the potential consequences of this new population per the birds’ evolution, ecology, and management. Ultimately, I suggest that this translocation is a long‐term benefit to the species.


| INTRODUC TI ON
There is a long history of translocation, a human-mediated movement and free release of wildlife by humans (Seddon et al., 2012(Seddon et al., , 2014. Animals may be transported for retention of population viability, assisted colonization, and several other species' conservation-related objectives (Evans et al., 2018;Seddon et al., 2014;Tobias et al., 2020). Translocations used as a conservation strategy have greatly increased in recent decades (Bouzat et al., 2009). Approximately 124 species were translocated worldwide from 1900 to 1992 but that increased to 424 species by 2005 (Seddon et al., 2007(Seddon et al., , 2014. Translocations often strive to reinforce existing populations or reintroduce a species into an area after a local extinction (Seddon et al., 2014;Thévenin et al., 2018). In some cases, a species may be moved beyond its endemic range for other purposes, such as establishing and growing a population of a huntable species, that is, Mottled Ducks (Anas fulvigula) in coastal South  (Kneece, 2016). Of the Mottled Ducks released to South Carolina, 26 originated from the Florida population and 1259 were from Louisiana and Texas (Kneece, 2016). Approximately 107 (8%) banded birds were later identified either through direct or indirect band recoveries from 1975 to 1986 (Kneece, 2016). Only 7 (6%) of these ducks  (Balkcom & Mixon, 2015;Lavretsky et al., 2021;Pollander et al., 2019). Prior to this introduction, there were apparently no records of Mottled Ducks breeding in South Carolina. Presently, Mottled Ducks inhabit at least South Carolina and Georgia, important regions to waterbirds of the South Atlantic Coastal Zone (SACZ; Gordon et al., 1998;Watson & Malloy, 2008). Given the apparent expanded range into Georgia, hereafter I will refer to this new population as SACZ Mottled Ducks (Seyoum et al., 2012) (Figure 1).
At the time of initial release in the 1970s, there was no genetic information available that differentiated West-Gulf Coast from Florida Mottled Ducks like that available today McCracken et al., 2001). Conservationists in the 1970s reconciled that the species would prosper in coastal South Carolina given some similarities in habitats used by Mottled Ducks in coastal Louisiana and Florida (Singleton, 1953;Smith, 1961). The release of Mottled Ducks into South Carolina, however, has created growing awareness in the waterfowl conservation community over potential genetic ramifications (Baldassarre, 2014;Seyoum et al., 2012). There is already concern over declining breeding populations of Mottled Ducks in some portions of its range (e.g., coastal Texas), mostly due to habitat contraction and loss (Wilson, 2007). As such, this release of birds into a novel environment arguably has diverse short-and long-term consequences and outcomes. Three specific negative concerns or hypotheses have been considered, including that currently established SACZ Mottled Ducks will: (1) Hybridize with feral Mallards; in North Carolina, for example, American Black Ducks (Anas rubripes) × Mallard introgression has resulted from gene flow through male feral Mallards Lawson et al., 2021); (2) hybridize with wild Mallards  (3) directly interbreed with the Florida Mottled Duck population, thereby disrupting this latter gene pool that has been generationally distinct (Bielefeld et al., 2010;Lavretsky et al., 2021;Peters et al., 2016). All three of these possibilities could occur and potentially deteriorate the integrity of the Florida Mottled Duck gene pool if subsequent hybrids or pure SACZ Mottled Ducks freely moved into Florida. A fourth and rather unknown result of this release rests with the Mottled Duck's ecological role and interactions with other species in their newly established wetland community (Table 1).

The current genetic structure of Mottled Ducks and other
Mallard-like species is well documented Peters et al., 2016;Weng, 2006). Although it is necessary to briefly overview those dynamics herein, my objective in this paper was to expand the view of the potential outcomes associated with this release (i.e., Table 1). In fact, I offer in the end that this new population is largely a long-term benefit for the species. conservation introduction, or the intentional movement and release of an organism outside its indigenous range (Hällfors et al., 2014;IUCN, 2013;Seddon, 2010). There are two components of conservation introductions, (a) Assisted colonization, or the intentional movement and release of an organism outside its indigenous range to avoid extinction of populations of the focal species, and (b) ecological replacement, or the intentional movement and release of an organism outside its indigenous range to perform a specific ecological function (IUCN, 2013). Despite these precise definitions, I submit that neither term applies here because genetics of Mottled Ducks, and the species' ecology for that matter, were not well established at the time of the release. Notwithstanding these definitions, Mottled Ducks were intentionally moved and released to establish a novel population, the potential outcomes of it being the subject of this paper.

| CONTEMP OR ARY S TATUS OF SAC Z MOT TLED DUCK S
The population status of SACZ Mottled Ducks is unknown, but available information suggests it has increased since initial release (Kneece et al., 2020 suggest an expanded regional population and achieving the original purpose, to grow the new population into a sustainable harvestable one. Population growth of these birds, however, has fueled concern over genetic integrity of the species, particularly that for Florida Mottled Ducks.  1986;Bielefeld et al., 2010;Mank et al., 2004;Peters et al., 2014;Stutzenbaker, 1988;USFWS, 2013). In support of limited hybridization or gene flow, Peters et al. (2014) explained that as much as four times more genetic diversity has likely resulted through gene flow between Mallards and Mottled Ducks, compared to the potential diversity achieved had they been completely isolated though time. An important alternative to this explanation, however, is that introgression of non-native genes could cause extinction of native genotypes that confer local adaptations TA B L E 1 A hypothetical model of potential consequences associated with introducing Mottled Ducks (n = 1285) from Florida and the West-Gulf Coast to coastal South Carolina, 1975Carolina, -1983 (Quilodrán et al., 2018) and maladaptive compared to their parentals.

| Mottled Duck genetics
Despite the potential negative implications of maladaptive alleles, Ford et al. (2017) recently estimated low levels (~5%-8%) of hybridization between Mallards and Mottled Ducks in the West-Gulf Coast, and this value was approximately 9% for Florida birds (Ford et al., 2017;Williams, Brust, et al., 2005;Williams, Fedynich, et al., 2005). Other studies demonstrated little contemporary gene flow among these Mallard-like species and posited that genetic extinction is unlikely for Mottled Ducks Weng, 2006

| Pipelining SACZ Mottled Duck genes into Florida
Another concern among some waterfowl conservationists is related to gene flow and that SACZ Mottled Ducks will introgress with Florida populations, ultimately eroding genetics of the latter (Baldassarre, 2014  sun-senti nel.com/news/weath er/hurri cane/sfl-hc-caneh istor y1,0,33520 10.special). Surprisingly, these significant storms apparently did not prompt Florida Mottled Ducks to settle (i.e., founder individuals) coastal South Carolina, a region boasting favorable habitats for the species for the past 400 years, specifically historic rice fields that eventually were converted to managed coastal wetlands (Edgar, 1998;Gordon et al., 1998;Zwank et al., 1989). Perhaps some individuals did move there but were too few to establish popula-

tions. Curiosity over the impacts of tropical cyclones on Mottled
Ducks has long existed, as molting birds have been killed in storms (Stutzenbaker, 1988

| Aspects of the introduction -The "unknown"
Perhaps a more challenging aspect of the introduction to be re-  (Cely et al., 1993;Kaufman, 1996). Mottled Ducks also nest in dense spartina and other vegetation amid seasonal wetlands (Kneece, 2016;Shipes, 2014). Undoubtedly, some fourth order (Johnson, 1980) resource needs of nesting Mottled Ducks will depart from several co-existing species. However, how these species partition foraging, and the potential influence of Mottled Ducks on nest clustering and density dependent nest survival (Ringelman et al., 2014) in this avian community are currently unknown but worthy of understanding.

| Novel environments and niche compatibility
Paradoxically, some degree of hybridization between species is good as genetic diversity may introduce variation, novel alleles, and mutations (Alleaume- Benharira et al., 2006;Frankham, 2005;Garant et al., 2007;Lande & Shannon, 1996). Low rates of gene flow (<2%) for years between two species of Darwin's Finches (Geospiza fortis and G. scandens) apparently enhanced beak morphology and overall fitness of the individuals (Grant & Grant, 2010;Hedrick, 2013;Lamichhaney et al., 2020). In effect, some levels of hybridization can assist adaptations to potentially new niches, and species can expand their climatic ranges resulting from introgression with other species (Krehenwinkel & Tautz, 2013;Stelkens et al., 2014). Peters et al. (2014) posited that introgression of Mallard alleles has helped maintain high genetic diversity in Mottled Ducks, which could benefit the adaptability and survival of the latter. Perhaps an unsettled question is how much gene flow between these populations is acceptable to conservationists? Attempts to safeguard the integrity of Florida Mottled Ducks seems a defensible conservation priority, but also a challenge, relative to evolutionary and ecological processes.  (Southwood, 1977 (Coster et al., 2018). Interestingly, hybridization between species likely occurs in marshes of intermediate salinity at some locations where range overlap occurs (Coster et al., 2018;Eddleman & Conway, 1994;Meanley, 1969;Olson, 1997).
Despite the threat of hybridization creating outbreeding depression, reduced fitness, or other consequences (Edmands, 2007;Rhymer & Simberloff, 1996), introgression likely introduced novel genotypes that increase fitness and potentially local adaptations (Coster et al., 2018;Rhymer & Simberloff, 1996). King and Clapper Rails co-exist in a region of Virginia and introgression is not viewed as deleterious, as Clapper Rails typically do not invade freshwater marshes, thus leaving this habitat type for King Rails (Coster et al., 2018).

Relative to Mottled Ducks, habitats used by Florida birds diverge somewhat from habitats in the West-Gulf Coast. Florida Mottled
Ducks historically have exploited thousands of ponds and irrigation reservoirs associated with ranching, farming, and citrus production inland and other suburban and urban areas (Bielefeld & Cox, 2006).
Further south near Lake Okeechobee, Mottled Ducks use stormwater treatment areas and permanent marshes of the Everglades (Bielefeld, 2008(Bielefeld, , 2011. The West-Gulf Coast Mottled Ducks also use freshwater wetlands, ditches, canals, and ricefields, but some birds in the West-Gulf Coast and South Carolina seek intermediate and brackish wetlands (Baldassarre, 2014;Grand, 1988;Shipes et al., 2015;Zwank et al., 1989). If SACZ Mottled Ducks (i.e., of predominate West-Gulf Coast origin) move seasonally or otherwise to Florida, it might be that these third-and fourth-order habitat affinities (Johnson, 1980) create natural niche partitioning among the cohorts of birds, similar to King and Clapper Rails in Virginia.
The evolutionary ecology of animal personalities (Dall et al., 2012;Miranda et al., 2013) may offer some insight into potential interactions between SACZ and Florida Mottled Ducks during their habitat use in Florida. Genetic components of animal personalities can influence resource use of individuals (Miranda et al., 2013;Schielzeth et al., 2011;Van Oers et al., 2004). Cities are evolutionarily novel environments with unfamiliar challenges for wildlife, and urban landscapes are thus ideal systems for understanding how plasticity might promote or hinder adaptation to new environments (Bressler et al., 2020;Shanahan et al., 2013;Sol et al., 2013). In dark-eyed juncos (Junco hyemalis) and Eurasian magpies (Pica pica), both demonstrated a protracted breeding season in urban areas, possibly resulting from milder climates or greater food abundances compared with their conspecifics in natural habitats (Bressler et al., 2020;Jerzak, 2001). What remains equivocal for birds generally is whether plasticity is adaptive for urban popula- Mottled Ducks in the West-Gulf Coast (Grand, 1988;Zwank et al., 1989 Carolina has lost approximately 29% of its wetlands since 1780 (Yarrow, 2009), and wetland losses are especially problematic along coastal South Carolina (Strauss et al., 2014). Moreover, states receiving the greatest levels of human migration from 1995 to 2000 included Georgia, Florida, and South Carolina, which increased the population density of coastal communities by 70% in those states between 1980between and 2003between (Franklin, 2003

| Are we stalling inbreeding depression?
West-Gulf Coast and Florida populations differ phenotypically (e.g., plumage and bill color) and are nearly as divergent from each other as they are from other Mallard-like duck taxa .
With modification to and foreseeable future loss of suitable habitats along coastal Carolina and in Florida, perhaps the most ecologically lucrative outcome of this translocation is that potential consequences of inbreeding depression have been delayed? Inbreeding depression is the mating of close relatives (Wright, 1922) and an artifact of it is expression of deleterious recessive alleles (Roff, 2002;Szulkin & Sheldon, 2007) and a trend toward genome-wide homozygosity (Keller & Waller, 2002;Szulkin & Sheldon, 2008).
Accumulation of deleterious mutations can subsequently reduce individual fitness (Opatová et al., 2016). Fortunately, there are potentially positive outcomes relative to inbreeding depression via individual dispersal. First, Opatová et al. (2016) studied effects of inbreeding on Zebra Finch sperm characteristics and inbred males had more abnormal spermatozoa and lower sperm velocity than outbred males maintained under the same conditions. Hence, dispersal of individuals from one population into another can increase the heterozygosity of a population and minimize breeding among close relatives (Hamilton & May, 1977;Opatová et al., 2016;Szulkin & Sheldon, 2008). Second, the Greater Prairie Chicken (Tympanuchus cupido pinnatus) has declined throughout its range in North America, in part due to issues with inbreeding depression (Bouzat et al., 2009 (Gordon et al., 1989(Gordon et al., , 1998. Our
However, the bird has an affinity for managed wetlands (Shipes et al., 2015), as do other dabbling ducks in coastal South Carolina (Gordon et al., 1998 (Taylor et al., 1993) can ameliorate many risk factors and allow physically disjunct populations to persist in a network (Crooks & Sanjayan, 2006;Macdonald & Johnson, 2001), or even as a metapopulation of interconnected habitats (Doleman, 2012;Hanski, 1999;Smith & Green, 2005;van Rees et al., 2018). In this light, SACZ Mottled Ducks are proximal to Florida, but at the same time the species demonstrates reluctance to move great distances, thus I hypothesize that population structuring will likely be maintained, but the limited gene flow that may occur could actually benefit both populations, with little fear of genetic homogenization to the Florida birds.
In closing, a primary concern for species viability is how availability of quality habitats influences population size and integrity. With